Fatty acid partitioning varies across fillet regions during sexual maturation in female rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) are commonly reared as diploids (2N, two sets of chromosomes) or triploids (3N, three sets of chromosomes). Sexual maturation in 2N has negative effects on production efficiency, nutrient retention, and fillet quality. On the other hand, 3N female rainbow trout fail to develop gonads, thus enabling an efficient extended growth period when production of larger fillets is desired. The objective of this study was to determine how fatty acid (FA) profiles of various tissue types change throughout development in 2N and 3N rainbow trout, with an emphasis on the response of different fillet regions. Diploid and 3N female rainbow trout were comingled and harvested at 10, 18, and 22months post hatch (mph) and FA profiles of the viscera, fillet sections, and fillet trimmings were analyzed. Diploid fish were larger (P<0.05) than 3N at all sampling periods. Fillet yield was similar between 2N and 3N at 10 and 18mph, while fillet yield was greater in 3N at 22mph (P<0.05). Fillets were divided into four sections; ventral, central, dorsal and caudal. In the ventral, dorsal, and caudal fillets, FAs continued to accumulate with age (P<0.05), regardless of ploidy. However, in the 2N ventral fillet the rate of muscle growth outpaced deposition of saturated FAs between 18 and 22mph (P<0.05). In the 2N central fillet the concentration of most FAs decreased between 18 and 22mph (P<0.05) while they continued to increase in 3N. A similar interaction occurred in viscera tissue, in which there was no net accumulation of FAs in 2N between 18 and 22mph while 3N continued to deposit FA. Saturated FAs were most susceptible to reduced concentrations during sexual maturation, suggesting an increased reliance upon these lipids as a source of energy to support gonad development. In conclusion, there was a disproportionate mobilization of FAs both across and within tissues, with lipids in the viscera and central fillet being particularly vulnerable to mobilization during sexual maturation.